Fix bug when overlaying middle arfs in multi-arf groups.
Fix bug when overlaying middle arfs in multi-arf groups.

Do not reset the alt ref active flag when overlaying the middle
arf(s) of a multi arf group.

Change-Id: Ia55a55a376973f3fd17161429fd2afb07b4df31f

Topopiccione/libvpx,webmproject/libvpx,jmvalin/aom,ittiamvpx/libvpx-1,Topopiccione/libvpx,Topopiccione/libvpx,thdav/aom,jmvalin/aom,smarter/aom,mwgoldsmith/libvpx,webmproject/libvpx,mwgoldsmith/libvpx,shacklettbp/aom,mwgoldsmith/vpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,shacklettbp/aom,luctrudeau/aom,mbebenita/aom,ittiamvpx/libvpx-1,shacklettbp/aom,smarter/aom,Topopiccione/libvpx,GrokImageCompression/aom,thdav/aom,ittiamvpx/libvpx-1,jmvalin/aom,ShiftMediaProject/libvpx,luctrudeau/aom,smarter/aom,shacklettbp/aom,shacklettbp/aom,ittiamvpx/libvpx-1,GrokImageCompression/aom,openpeer/libvpx_new,mbebenita/aom,mwgoldsmith/vpx,mwgoldsmith/vpx,mbebenita/aom,mbebenita/aom,ShiftMediaProject/libvpx,mwgoldsmith/vpx,mbebenita/aom,mbebenita/aom,Topopiccione/libvpx,webmproject/libvpx,mbebenita/aom,mwgoldsmith/libvpx,luctrudeau/aom,Topopiccione/libvpx,mbebenita/aom,GrokImageCompression/aom,openpeer/libvpx_new,luctrudeau/aom,jmvalin/aom,GrokImageCompression/aom,mwgoldsmith/libvpx,openpeer/libvpx_new,shacklettbp/aom,ShiftMediaProject/libvpx,smarter/aom,ittiamvpx/libvpx-1,openpeer/libvpx_new,webmproject/libvpx,smarter/aom,luctrudeau/aom,mwgoldsmith/vpx,webmproject/libvpx,jmvalin/aom,thdav/aom,thdav/aom,ittiamvpx/libvpx-1,GrokImageCompression/aom,ShiftMediaProject/libvpx,jmvalin/aom,GrokImageCompression/aom,thdav/aom,openpeer/libvpx_new,luctrudeau/aom,ShiftMediaProject/libvpx,smarter/aom,thdav/aom,openpeer/libvpx_new,mbebenita/aom,mwgoldsmith/libvpx,webmproject/libvpx